Up to the present time, there are two principal ways of manufacturing thin layers of ceramics composed of one or more metal oxides such as alumina, silica, titanium oxide, potassium oxide, etc. . . .
A first method consists of mixing very fine powders of each of the corresponding oxides in determined proportions, then in suspending them in an organic binding agent or any other binding agent so as to obtain a slip adapted to be deposited on a support in a very thin layer, before being sintered.
This first method requires careful monitoring of the granulometry of the oxide powders as well as of the physico-chemical properties of the slip.
Depending on whether or not the support on which the thin layer of slip is deposited is porous, the viscosity of the slip and its concentration of organic products (binding agents, plasticizers, surface-active agents, . . . ) must be monitored with very high precision in order to allow the physico-chemical and mechanical characteristics of the deposited layer to be perfectly reproduced.
A second method employs the sol-gel technique which leads to obtaining a sol composed of metal-organic precursors, i.e. polymers containing metal cores connected to organic groups. By an appropriate heat treatment, these polymers are decomposed to produce the corresponding metal oxides.
According to this second method, a solution is formed, composed of metal oxide hydrates or of partially hydrolyzed metal alkoxides and this solution is deposited in a thin layer on a substrate which is porous or not. This solution has well-defined viscosity and characteristics and leads, by slow drying at low temperature, to a polymer gel which is constituted by a perfectly cross-linked metal-organic lattice.
After drying, the thin layer of gel is subjected to a heat treatment which converts it into a thin membrane composed of metal oxides. This second method makes it possible to obtain membranes which are much more homogeneous and of better quality than those obtained by the first method, which is conventional with ceramists.
The processes according to the invention are allied to both methods.
The processes according to the invention enable thin membranes to be manufactured which are composed of an inorganic lattice of titanium and silicon oxides.
They make it possible to obtain either a submicronic powder composed of mixed metal oxides whose granulometry may be perfectly monitored and which makes it possible to produce a slip applicable on a support according to the first method, or a solution applicable in thin layer on a support making it possible to obtain by heat treatment a membrane whose porosity may be monitored as desired from the respective proportions of titanium and silicon.
It is an object of the invention to provide means for depositing on supports very reactive submicronic layers making it possible to obtain, by heat treatment, membranes which are microporous or not, at sintering temperatures lower than those usually required, hence a saving in baking energy and a better porosity.